1. Field of the Invention
The present invention relates to a color video camera. More specifically, the present invention relates to a color video camera which utilizes a solid-state image sensing device having a large number of pixels arranged in a matrix fashion and a plurality of color filters arranged in a mosaic fashion.
2. Description of the Prior Art
In such a kind of color video camera, a color filter of a predetermined color (for example, any one of R, G and B) is arranged for each pixel, and by processing signals from a solid-state image sensing device, a color separation is performed such that video signals of R, G and B can be produced.
A case where a color filter of G and a color filter of R are alternately arranged in a horizontal direction as shown in FIG. 1(B) is assumed, for example. Since no G signal is obtained from a specific pixel on which the color filter of R is arranged, by performing interpolation calculation with using G signals from pixels adjacent to the specific pixel, a G signal of the specific pixel is obtained. That is, by calculating an average of signals from the pixels of G which sandwich the pixel of R in FIG. 1(B), the G signal at the pixel of R can be obtained. As well known, such a method is a method utilizing a correlation in the horizontal direction. However, it is known that in such a simple interpolation method, a false color signal is produced at a boundary (edge) where a white portion and a black portion are adjacent to each other.
A case where an incident light shown in FIG. 1(A) is applied to the solid-state image sensing device having a color filter arrangement shown in FIG. 1(B) is assumed. The incident light suddenly changes from white to black as shown in FIG. 1(A). Signal levels from respective pixels at that time are shown in FIG. 1(C). The G signal and the R signal are "1.0", respectively, at the white portion and are "0", respectively, at the black portion. In such a case, if the above described interpolation method is applied, the G signal after interpolation and the R signal after interpolation become "1.0" and "0.5", and "0.5" and "0.0", respectively, at the boundary of the white portion and the black portion as shown in FIG. 1(D) and FIG. 1(E). On the other hand, the G signal and the It signal must originally have levels shown in FIG. 1(F) and FIG. 1(G). Therefore, it will be understood that in FIG. 1(D) and FIG. 1(E), false color signals are produced at the edge.
As a counter measure for such a false color signal, a method utilizing a low-pass filter, or a method suppressing a color signal at the boundary (edge) has been proposed. There is a prior art in connection to the latter method, which is Japanese Patent Application No. 4-68361 filed on Mar. 26, 1992, which is assigned to the same assignee of the present invention.
In the former method, a level of the false color signal can be lowered, but an area where the false color signal is produced is enlarged. Furthermore, in the latter method, a color signal which is to be originally obtained is suppressed together with the false color signal, and therefore, there is an occasion that no color is obtained at the boundary (edge).